1. Field of the Invention
This invention relates to a process for obtaining valuable metals such as copper, nickel, cobalt and the like by selectively reductively roasting deep sea manganese nodules and extracting these metals with an aqueous ammoniacal solution and to a purification process for removing iron and manganese from the leach solution.
2. Description of Prior Art
Manganese nodules are distributed widely on deep sea bottoms at a depth of several thousand meters. They have granular, nodular or plate forms and contain manganese and iron as the main ingredients together with metals such as nickel, copper, cobalt and the like in the form of hydroxides. Manganese nodules are distributed widely on the bottom of the Pacific Ocean and the Atlantic Ocean. It has been estimated from data available at present that there are 1,700 billion tons of manganese nodules on the bottom of the Pacific Ocean which include nickel in an amount of 15 to 20 billion tons, copper in an amount of 7 to 10 billion tons and cobalt in an amount of 5 billion tons. The nodules are composed approximately, by weight, of 25% of Mn, 15% of Fe, 1% of Ni, 0.5% of Cu and 0.2% of Co.
The presence of manganese nodules has been known since the end of the 19th century but no attempt has been commercially made with respect to the recovery of the metals therefrom. Such manganese nodules are supposed to be a composite ore for which no known extractive metallurgy can be applied at present. An attempt to recover not only the manganese, but also the nickel, copper, cobalt and the like has been just begun, but there has been carried out no test on commercial scale nor development of any treatment for the manganese nodules which can recover all of the metal values therefrom.
Various processes have been studied for treating manganese nodules, including (1) leaching the ore directly with a mineral acid such as sulfuric acid or the like, (2) leaching the reduced ore with a mineral acid, (3) chloridizing volatilization, (4) segregation, (5) reductively smelting, and (6) extracting the reduced ore with an aqueous ammoniacal solution. However, there are many problems with such processes. For example, the process for leaching the reduced ore with an acid disadvantageously requires an increased amount of acid due to the dissolution of a large amount of manganese in the acid, and the separation of manganese from nickel and the like is difficult in the resulting aqueous solution. When the ore is melted, separation and recovery of nickel, cobalt and copper from the resulting crude metals is difficult. When the reduced ore is extracted with an aqueous ammoniacal solution, a large amount of manganese is dissolved in the leach solution and not only are there problems in separating manganese and iron from the aqueous solution, but the yields of nickel, copper and cobalt are not high.
It is thus an object of this invention to recover valuable metals such as nickel, copper, cobalt and the like and to recover a raw material for use in the preparation of ferromanganese from manganese nodules. It is another object to provide an extraction process wherein the efficiency is improved with respect to the extraction of reduced manganese nodules with an aqueous ammoniacal solution by reducing at least the nickel, cobalt and copper to the metallic state while selectively reductively roasting the nodules. It is a further object to provide a purification process for removing most of the iron and manganese solved in the leach solution to purify the aqueous ammoniacal solution. Other objects and features of this invention will be apparent from the following description.